ProjectAbstract: SCD is a genetic blood disorder characterized by abnormal hemoglobin S (HbS) synthesis with sickle cell anemia (SCA) as the most common subtype. Stroke is the most frequent cause of death and long-term disabilityinbothchildrenandadultswithSCD.Studiesofpatientswithfocalneurologicdeficitshaverevealed abnormalities of both large and small vessels in SCD. Currently, the main clinical screening test is the use of transcranialDoppler(TCD)forneurologicallyasymptomaticchildrenwithSCD.TheTCDtestisnoteffectiveto screenstrokeriskinadultSCDpatients.Cerebraloxygenextractionfraction(OEF),theratiobetweenoxygen consumption and delivery, has been recognized as a potentially more sensitive and specific indicator of cerebrovascularimpairmentinSCD.OEFmeasurementbasedonT2-oximetryMRIispromisingasitdoesnot require a contrast agent and is free of radiation. The existing T2-oximetry MRI techniques are not yet able to reliablymeasurethebloodoxygenationinsmallveins.However,thebloodoxygenationinthesesmallveinsis more sensitive to local neurological vasopathology. Using our recently developed velocity-selective MR angiographytechnique(thatpreserveshighbloodsignalwhilesuppressingtissuesignal),weaimtofillthisgap by developing a fast and reliable protocol for quantitative OEF venography including the small veins. This will helptoestablishtheroleofOEFforstrokepreventionamongadultSCDpatients.Theoverallobjectivesofthis projects are: 1) to develop and validate a robust T2-oximetry MRI protocol and demonstrated its reliability, reproducibility and accuracy in healthy volunteers. 2) to build a SCD specific T2 calibration model that can reliablytranslatethemeasuredMRIparameter(bloodT2)tobloodoxygenation.3)tomeasurethewholebrain andregionalcerebralOEFbeforeandaftertransfusioninSCDpatientswithahistoryofstroketohaveapilot studyontherelationshipbetweenbetweenOEFandthebraininjury(silentcerebralinfarctionandstroke).